1. Field of the Invention
The present invention relates to a hybrid power unit that is mounted on a vehicle body frame of a saddle-type vehicle and includes an engine having a crankcase that rotatably supports a crankshaft, a transmission that has a transmission shaft parallel to the crankshaft and is housed in a transmission chamber formed in the crankcase below the crankshaft, a clutch system that enables switching between connection and disconnection of power transmission from the crankshaft to the transmission shaft, and an electric motor capable of transmitting rotational power to the transmission shaft.
2. Description of Background Art
A hybrid motorcycle is known wherein a hybrid power unit having an engine and an electric motor is mounted on a vehicle body frame. See, for example, Japanese Patent Laid-Open No. 2011-73627.
However, in the hybrid power unit disclosed in the above-mentioned Japanese Patent Laid-Open No. 2011-73627, the electric motor is directly joined to the crankshaft of the engine coaxially. Thus, when an operation by the electric motor alone is attempted, the engine is dragged and the load becomes large. For this reason, it has been a challenge to effectively set use at the best point of the motor efficiency and enlarge the range in which the efficiency is favorable.
It is conceivable that, in order to solve such a problem, the rotational power from the electric motor rendered incapable of direct power transmission from and to the crankshaft is transmitted to the transmission shaft of the transmission. However, when the electric motor is disposed coaxially with the transmission shaft, the crankcase becomes large toward the lower side and the vehicle height of the saddle-type vehicle becomes high. For this reason, it is required to dispose the rotation axis line of the electric motor on the upper side relative to the transmission shaft and a power transmission mechanism needs to be provided between the electric motor and the transmission shaft. In this case, the power transmission mechanism bears a comparatively-large load and thus needs to be lubricated and it is conceivable that the power transmission mechanism is lubricated by lubricating oil in the transmission chamber in which the transmission is housed. However, if part of the rotor of the electric motor soaks in the lubricating oil, rotation resistance arises, which causes the lowering of the efficiency. Thus, it is also conceivable that separation between the electric motor and the power transmission mechanism is made by a wall through which a motor shaft that is coaxially continuous with the rotor is made to liquid-tightly penetrate. However, this causes a problem wherein the size of the hybrid power unit increases in the direction along the axis line of the crankshaft.